The present invention relates to an air cooled internal combustion engine and, more particularly, to an air cooled internal combustion engine the size of which is reduced without being accompanied by deterioration of the engine performance.
Generally speaking, an air cooled single cylinder internal combustion engine for general purposes has a cooling fan provided unitarily with a flywheel, so that the cooling fan case covering this cooling fan is located at the same side as the flywheel. Therefore, the suction side air cleaner for introducing fresh air and the exhaust silencer of the engine are disposed at the opposite side of the engine to the valve actuating mechanism such as cam shaft and so forth and are directed in the same directions. On the other hand, in order to meet the demand for reducing the size of the engine, the air cleaner and the silencer, which are directed in the same direction, are arranged to make an interference with each other.
For this reason, the air cleaner and the silencer are allowed to have only limited capacities resulting in a correspondingly reduced engine performance.
Also, the cooling air induced by the cooling fan has to be delivered to both of the cylinder head and the cylinder block, without concentrating to either one. In order that this air is sufficiently distributed to both of the cylinder head and the cylinder block, the size of the mechanism is increased inevitably due to restriction of the positions of intake and exhaust ports, to undesirably hinder the reduction of the size of the engine.
Usually, the push rod cover which covers the push rods for pushing up valve arms for opening and closing the intake and exhaust valves is formed separately from the cylinder block. Therefore, the number of parts is inconveniently increased to make it difficult to reduce the engine size and, in addition, there is a tendency that oil is undesirably leaked through the upper and lower seal portions between the cylinder block and the cylinder head.
Due to the limitation of the mounting space, the silencer attached to the exhaust port is usually mounted to largely project to the outside of the engine, which not only hinders the reduction of engine size but also poses a problem concerning the mechanical strength.
In case of a diesel engine, it is a common measure to dispose the tappet for actuating a fuel injection pump between the tappet for intake valve and the tappet for exhaust valve, in order to reduce the length of the engine. In such an arrangement, it is necessary to preserve a considerably large distance between the intake and exhaust valves. Thus, this arrangement not always contributes to the reduction of size of the engine.
Usually, a recoil starter is attached to the aforementioned cooling fan case which in turn is attached to the engine body by means of bolts. Therefore, it is extremely difficult to attach the cooling fan case in a manner to avoid vibration. Thus, the cooling fan case poses a problem of noise, as well as increase of production cost. The same applies also to the attaching of a fuel tank to the engine body. Namely, the number of parts is increased, as well as the production cost, to require a complicated and troublesome assembling work.